Compact sleeve‐gun source arrays

Geophysics ◽  
1991 ◽  
Vol 56 (3) ◽  
pp. 402-407 ◽  
Author(s):  
P. M. Fontana ◽  
T.‐A. Haugland
Keyword(s):  
Small Volume ◽  
Spectral Characteristics ◽  
Seismic Source ◽  
Pulse Amplitude ◽  
Operational Efficiency ◽  
Far Field ◽  
Air Compressor ◽  
Air Gun ◽  
Marine Seismic

Data derived from far‐field signature measurements have inspired several guidelines for using clustered sleeve guns effectively in tuned marine seismic source arrays. Primarily, these data show that for a given volume the signature produced by a cluster of sleeve guns has a comparable bubble period, increased primary amplitude, and reduced bubble‐pulse amplitude compared to the signature of a single gun. These results agree with those reported for clusters of conventional air guns. However, when the data are analyzed in terms of acoustic and operational efficiency, we find that for array elements with volumes greater than [Formula: see text] two‐gun clusters are more desirable than equivalent volume clusters of several small volume guns. For array elements with volumes up to [Formula: see text], the data show no significant advantages for using clusters instead of single guns. These guidelines have led to the design of sleeve‐gun arrays that produce signatures with temporal and spectral characteristics equal to or exceeding those produced by conventional air‐gun arrays incorporating almost twice the total gun volume. Moreover, these new arrays operate with a total number of individual guns comparable to conventional arrays, thus improving the performance of source arrays on small survey vessels without having to increase air compressor capacity or ancillary source equipment.

Seismic source decomposition

Geophysics ◽  
1983 ◽  
Vol 48 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Paul L. Stoffa ◽  
Anton Ziolkowski
Keyword(s):  
Point Source ◽  
Spectral Characteristics ◽  
Patent Application ◽  
Power Spectra ◽  
Seismic Source ◽  
Three Dimensions ◽  
Far Field ◽  
Air Gun ◽  
Power Spectral ◽  
Directional Characteristics

We exploit the differences that exist between the radiation fields of a point source and an array to design a time‐separated marine seismic source array with desired power spectral and directional characteristics, whose far‐field time signature is known precisely from measurements. The desired power spectral characteristics are created by firing a predetermined series of point source units sequentially, such that their time signatures do not overlap. The effective power spectrum of the whole series of time‐distributed signatures can be made to approximate the sum of the power spectra of the individual signatures and can, therefore, be designed to suit the desired application by the appropriate choice of source units. The desired directional characteristics of the array can be created by arranging the source unit separations such that each source unit reaches the desired spatial position at the prescribed firing instant. The key to the subsequent processing of the recorded data is to measure the pressure wave generated by each point source unit with a hydrophone placed close by, but in the linear radiation field. The position of this hydrophone relative to the source unit must be known accurately in all three dimensions. The depths of the source units and their relative spatial positions at the instants of firing must also all be known. From these measurements the far‐field signature of the sequence in any azimuth can be deduced, and the impulse response of the earth can be recovered by dividing the Fourier frequency spectrum of the recorded reflection data by that of the measured source unit sequence. This process is completely deterministic in nature and depends primarily upon our ability to monitor accurately the far‐field signature of each source unit. Field results from an initial evaluation of this method indicate that this measurement can be readily accomplished. The success of this technique is then ultimately dependent on the signal to noise ratio. [This method is the subject of a patent application.] We stress that, since the signature is known, we are not obliged to make any assumptions about the phase. In particular, we do not need to make the minimum‐phase assumption. We are therefore free to choose our parameters to optimize our desired power spectral and directional characteristics with complete disregard for the conventional requirement that the signature of an air gun source have a high primary‐to‐bubble ratio.

The shape of things to come — Development and testing of a new marine vibrator source

2019 ◽  
Vol 38 (9) ◽  
pp. 680-690 ◽  
Author(s):  
Benoît Teyssandier ◽  
John J. Sallas
Keyword(s):  
Seismic Source ◽  
Test Facility ◽  
Data Sets ◽  
Far Field ◽  
Ocean Bottom ◽  
Air Gun ◽  
Seismic Image ◽  
Field Radiation ◽  
Technical Issues ◽  
To Come

Ten years ago, CGG launched a project to develop a new concept of marine vibrator (MV) technology. We present our work, concluding with the successful acquisition of a seismic image using an ocean-bottom-node 2D survey. The expectation for MV technology is that it could reduce ocean exposure to seismic source sound, enable new acquisition solutions, and improve seismic data quality. After consideration of our objectives in terms of imaging, productivity, acoustic efficiency, and operational risk, we developed two spectrally complementary prototypes to cover the seismic bandwidth. In practice, an array composed of several MV units is needed for images of comparable quality to those produced from air-gun data sets. Because coupling to the water is invariant, MV signals tend to be repeatable. Since far-field pressure is directly proportional to piston volumetric acceleration, the far-field radiation can be well controlled through accurate piston motion control. These features allow us to shape signals to match precisely a desired spectrum while observing equipment constraints. Over the last few years, an intensive validation process was conducted at our dedicated test facility. The MV units were exposed to 2000 hours of in-sea testing with only minor technical issues.

Some notes on air-gun development as a marine seismic source

2009 ◽  
Vol 28 (11) ◽  
pp. 1334-1335 ◽  
Author(s):  
Ben F. Giles
Keyword(s):  
Seismic Source ◽  
Air Gun ◽  
Marine Seismic

Design of Near-orthogonal Air-gun Sequences for Marine Seismic Source Encoding

2016 ◽  
Author(s):  
M.B. Mueller ◽  
D.F. Halliday ◽  
D.J. van Manen ◽  
J.O.A. Robertsson
Keyword(s):  
Seismic Source ◽  
Air Gun ◽  
Marine Seismic ◽  
Source Encoding

Single water gun far‐field pressure signatures estimated from near‐field measurements

Geophysics ◽  
1985 ◽  
Vol 50 (2) ◽  
pp. 257-261 ◽  
Author(s):  
M. H. Safar
Keyword(s):  
High Resolution ◽  
Data Acquisition ◽  
Seismic Data ◽  
Near Field ◽  
Field Measurements ◽  
Reference Source ◽  
Far Field ◽  
Air Gun ◽  
Seismic Data Acquisition ◽  
Marine Seismic

An important recent development in marine seismic data acquisition is the introduction of the Gemini technique (Newman, 1983, Haskey et al., 1983). The technique involves the use of a single Sodera water gun as a reference source together with the conventional air gun or water gun array which is fired a second or two after firing the reference source. The near‐field pressure signature radiated by the reference source is monitored continuously. The main advantage of the Gemini technique is that a shallow high;resolution section is recorded simultaneously with that obtained from the main array.

PC‐based acquisition and processing of high‐resolution marine seismic data

Geophysics ◽  
1996 ◽  
Vol 61 (6) ◽  
pp. 1804-1812 ◽  
Author(s):  
Ho‐Young Lee ◽  
Byung‐Koo Hyun ◽  
Young‐Sae Kong
Keyword(s):  
High Resolution ◽  
Seismic Data ◽  
Spectral Characteristics ◽  
Processing System ◽  
Band Pass Filter ◽  
Pass Filter ◽  
Optical Disk Drive ◽  
Air Gun ◽  
Marine Seismic

We have improved the quality of high‐resolution marine seismic data using a simple PC‐based acquisition and processing system. The system consists of a PC, an A/D converter, and a magneto‐optical disk drive. The system has been designed to acquire single‐channel data at up to 60,000 samples per second and to perform data processing of seismic data by a simple procedure. Test surveys have been carried out off Pohang, southern East Sea of Korea. The seismic systems used for the test were an air gun and a 3.5 kHz sub‐bottom profiling system. Spectral characteristics of the sources were analyzed. Simple digital signal processes which include gain recovery, deconvolution, band‐pass filter, and swell filter were performed. The quality of seismic sections produced by the system is greatly enhanced in comparison to analog sections. The PC‐based system for acquisition and processing of high‐resolution marine seismic data is economical and versatile.

Source signature encoding of a vertical source array to separate the emitted direct wave from its ghost

Geophysics ◽  
2018 ◽  
Vol 83 (4) ◽  
pp. P9-P18
Author(s):  
Moritz B. Mueller ◽  
David F. Halliday ◽  
Dirk-Jan van Manen ◽  
Johan O. A. Robertsson
Keyword(s):  
Seismic Source ◽  
Opposite Polarity ◽  
Direct Wave ◽  
Air Gun ◽  
Short Period ◽  
Separate Source ◽  
Marine Seismic ◽  
Separation Feature ◽  
Marine Air ◽  
Simultaneous Source

Marine air-gun sources can be sequence-encoded by firing their individual elements independently over a short period of time. Using near-orthogonal firing sequences, whose crosscorrelation is minimal, as encoding sequences for multiple sets of air-gun sources, enables us to exploit their orthogonality as a separation feature. We find that, by distributing air guns over depths from 5 to 30 m, firing sequences can be designed whose direct, down-going wavefield is close to orthogonal to its source-ghost wavefield. The fundamentally new aspect of this approach is that the source-ghost signal is no longer just a time-delayed, opposite-polarity version of the down-going wavefield, but due to the different air-gun depths results in a different source sequence. This enables the consideration of the ghost wavefield as a separate source. We generate a set of such firing sequences by minimizing the crosscorrelation of these wavefields and optimizing their respective autocorrelations to achieve sharp peaks. The obtained, optimized firing sequences are then used for marine seismic source encoding. By adapting a multifrequency algorithm originally developed for simultaneous source separation, we determine that the ghost-source wavefield can be separated as a separate source from the direct, down-going wavefield.

A standard quantitative calibration procedure for marine seismic sources

Geophysics ◽  
1985 ◽  
Vol 50 (10) ◽  
pp. 1525-1532 ◽  
Author(s):  
J. R. Fricke ◽  
J. M. Davis ◽  
D. H. Reed
Keyword(s):  
Energy Flux ◽  
Spectral Characteristics ◽  
Seismic Energy ◽  
Seismic Source ◽  
Calibration Procedure ◽  
National Standards ◽  
Computer Algorithms ◽  
Source Evaluation ◽  
Transient Nature ◽  
Marine Seismic

Marine source evaluation has traditionally been a subjective and qualitative study. This is particularly true in the case of source spectral characteristics. As a result, source evaluation, development, and array design based on seismic energy over a specified frequency band have been impossible. Further, the transient nature of source wavelets lends itseft to energy analysis rather than the traditional relative power analysis. The methodology required to achieve a calibrated quantitative estimate of marine seismic source energy is detailed here. The procedure involves two steps. First, a calibrated high‐fidelity measurement of the source signature is required; and second, an analysis of the signatures by a suite of computer algorithms designed to extract quantified measures of amplitude and energy is necessary. Results of the analysis include a time‐domain signature calibrated in American National Standards Institute (ANSI) units of pressure and a frequency domain spectrum calibrated in ANSI units of energy flux. These results provide figures of merit for evaluation of individual source characteristics (e.g., energy flux over seismic bandwidth, and total source energy). Additionally, the results provide data for a quantitative comparison of any two or more sources. Illustrative examples of source studies are included.

Implementation of marine seismic source wavefields in finite-difference methods using wavefield injection

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. T211-T219 ◽  
Author(s):  
Kjetil E. Haavik ◽  
Espen Birger Raknes ◽  
Martin Landrø
Keyword(s):  
Finite Difference ◽  
Finite Difference Methods ◽  
Waveform Inversion ◽  
Seismic Source ◽  
Injection Technique ◽  
Surface Reflection ◽  
Air Gun ◽  
True Source ◽  
Grid Points ◽  
Marine Seismic

We have developed a method for implementing source wavefields in finite-difference (FD) schemes for marine seismic modeling, migration, and inversion. By using the wavefield injection technique, it is possible to inject arbitrary source wavefields into an FD grid. We have assumed that the notional source signatures from each gun in an air-gun array and their positions are known. The source wavefield is extrapolated to a specified surface below the true source positions using analytical Green’s functions. On this surface, the pressure and its vertical derivative are inserted into the FD grid. The wavefield propagating from this surface will then propagate downward and appear as if it came from the true source position. The source positions do not need to coincide with the FD grid points, and the free-surface reflection coefficient for the source ghost can be specified; i.e., it can deviate from [Formula: see text], and it can be frequency dependent. These features are possible because of the analytical extrapolation step. The presented method allows modeling of any kind of marine seismic source as long as the notional source signature and radiation pattern from each individual source element is known. A simple full-waveform inversion example shows that it is important to honor the source geometry in forward modeling of seismic data.

scholarly journals On low frequencies emitted by air guns at very shallow depths — An experimental study

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. P61-P71 ◽  
Author(s):  
Daniel Wehner ◽  
Martin Landrø ◽  
Lasse Amundsen
Keyword(s):  
Large Volume ◽  
Field Experiments ◽  
Field Measurements ◽  
Seismic Source ◽  
Sea Surface ◽  
Frequency Signal ◽  
Low Frequencies ◽  
Air Gun ◽  
Seismic Acquisition ◽  
Marine Seismic

In marine seismic acquisition, the enhancement of frequency amplitudes below 5 Hz is of special interest because it improves imaging of the subsurface. The frequency content of the air gun, the most commonly used marine seismic source, is mainly controlled by its depth and the volume. Although the depth dependency on frequencies greater than 5 Hz has been thoroughly investigated, for frequencies less than 5 Hz it is less understood. However, recent results suggest that sources fired very close to the sea surface might enhance these very low frequencies. Therefore, we conduct dedicated tank experiments to investigate the changes of the source signal for very shallow sources in more detail. A small-volume air gun is fired at different distances from the water-air interface, including depths for which the air bubble bursts directly into the surrounding air. The variations of the oscillating bubble and surface disturbances, which can cause changes of the reflected signal from the sea surface, are explored to determine whether an increased frequency signal below 5 Hz can be achieved from very shallow air guns. The results are compared with field measurements of a large-volume air gun fired close to the sea surface. The results reveal an increased signal for frequencies below 5 Hz of up to 10 and 20 dB for the tank and field experiments, respectively, for the source depth at which the air gun bubble bursts directly into the surrounding air. For large-volume air guns, an increased low-frequency signal might also be achieved for sources that are slightly deeper than this bursting depth. From these observations, new design considerations in the geometry of air-gun arrays in marine seismic acquisition are suggested.

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